(1) Field of the Invention
The present invention relates to a novel oil adsorbent suitable for oil-removing purification treatment of oil-contaminated water, a process for preparation thereof and uses of this novel oil adsorbent.
By the term "oil-contaminated water" used herein is meant industrial waste water having a relatively high oil content, which is discharged from a petroleum refinery or other factory waste water from ships, supply water from oil-contaminated water sources, and water of oil-contaminated rivers, lakes, bays and oceans.
Treatment of contaminated waters is very important for prevention of environmental pollution, and various attemps have heretofore been made to remove oils from oil-contaminated waters. Since regulations on disposal of waste waters are now very rigorous, development of effective and economical methods for the treatment of oil-contaminated waters is eagerly desired.
(2) Description of the Prior Art
Various methods have heretofore been proposed for the treatment of oil-contaminated waters, easpecially oil-containing waste water. For example, there can be mentioned (1) a gravity separation method in which oil-containing waste water is kept stationary in a tank, oil drops contained in the waste water are caused to rise to the surface by virtue of the difference in specific gravity and the oil drops are separated by, for example, a separator of the API or CPI type, (2) a flocculating separation method or coagulation process in which a flocculant such as aluminum sulfate, an iron salt or the like is added to oil-containing waste water to adjust the pH and destroy the oil emulsion phase, and oils are co-precipitated together with solids formed by the reaction in the form of flocs, and (3) an air floatation method in which compressed air is blown into waste water to generate air bubbles in the waste water and oils are caused to rise in the state carried by the air bubbles.
These known methods, however, are defective in various points. For example, the method (1) is not substantially effective for the treatment of waste waters containing emulsified oils, especially those having emulsified oil drops of a size smaller than about 60 microns, and further, a vast area is necessary for practising the method (1). The method (2) is advantageous in that not only free oils but also emulsified oils can be separated, but the method also requires a vast area for its practising and is defective in that the treatment of flocs involves difficulties. The method (3) is not suitable for the treatment of large quantities of waste waters.
In short, each of these known methods is disadvantageous from the economical view-point and the treatment cost is high, and no satisfactory results can be obtained when contaminated water containing oils at relatively high contents and discharged in large quantities, such as waste waters from petroleum refinery are treated.
There is also known an adsorption separation method using an oil adsorbent. As the oil adsorbent applicable to this method, there are known solid granular adsorbents formed by subjecting polymers such as polyesters, polyvinyl chloride, polystyrene and polyolefines to certain treatments. For example, a solid granular product manufactured by Chiba Fine Chemical Co., Tokyo, Japan is commercially available under the tradename "PIC" as the polyolefine-type oil adsorbent. These commercial oil adsorbents are considerably effective, and the method using such oil adsorbent is advantageous over the above methods (1), (2) and (3) in the point that the effect of reducing the oil content in waste water can be attained assuredly by a simple operation with the use of a treatment apparatus having a relatively compact structure. This adsorption separation method, however, is still insufficient. More specifically, an oil adsorbent such as mentioned above is relatively expensive and the regeneration treatment for reactivating the once used adsorbent is very troublesome and involves high costs. In general, therefore, the once used oil adsorbent is discarged or burnt, and hence, the method is also not advantageous from the economical view-point. In order to regenerate the once used oil adsorbent, it is necessary to adopt a complicated method. For example, the used adsorbent is treated with a solvent to dissolve only the adsorbed substances (oils) into the solvent and regenerate the adsorbent, and if necessary, the adsorbed substances are separated and recovered from the solvent. Alternately, the adsorbed substances are separated from the adsorbent by heating or mild reaction with water vapor or other gas to thereby regenerate the adsorbent. Such regeneration treatment is very troublesome and costs much money, and hence, the conventional adsorption separation method is economically unsatisfactory. Therefore, development of a cheap oil adsorbent having a high adsorbing property and being capable of being regenerated with ease has been desired in the art.